1. Field of the Invention
The present invention generally relates to electronic circuits and, more specifically, to the protection of data manipulated by an electronic circuit integrating a processor and at least one non-volatile memory.
The present invention especially applies to chip cards and other secure integrated circuits.
2. Discussion of Related Art
Chip cards, or more generally so-called secure integrated circuits, are generally equipped with an integrated circuit comprising a microprocessor and several memories, among which a non-volatile and volatile memories.
Such devices manipulate so-called secret data, that is, data to which only one or several users are allowed to access. It is generally spoken of secret keys, which are used by encryption algorithms to protect or to authenticate data (messages, images, video, etc.).
The secret data are generally stored in a non-volatile memory of the integrated circuit and are considered as protected within this memory.
A weak point of such devices is that when the keys have to be manipulated by the circuit processor, they are likely to transit over a data bus shared by the microprocessor and other elements of the circuit, and risk being pirated, for example, by so-called side channel attacks which examine, for example, the circuit consumption, its radiation, etc.
Various methods have already been provided to try to protect the keys manipulated by a secure circuit.
For example, document EP-A-1880387 describes a system for protecting a memory against fault injection attacks.
It has also already been provided to encrypt transmissions over the bus. This avoids a possible piracy during the transfer between the memory and the processor registers.
However, due the advance in data piracy, the vulnerability when data are manipulated by the circuit processor has increased. Even if the secret data are most often masked by random numbers or other protection solutions, there is a time when they plainly appear in one of the processor registers. Recent studies have shown that it was then possible to pirate these critical data from such registers.